Coating of alumina onto the surface of hollow glass spheres was accomplished by controlled heterogeneous precipitation from aqueous solutions. The processing conditions were optimized to yield thin and uniform precursor coatings. After calcination, converting the precursor to alumina, the alumina-coated hollow glass spheres formed free-flowing powders that were used to produce glass/alumina composites with up to 35 vol% of controlled and well dispersed closed porosity. The dielectric constants and the flexural strengths of such porous composites were determined as a function of porosity.